Passive diffusion samplers are known in the art. As background, U.S. Pat. No. 5,804,743 to Vroblesky et al., which is hereby incorporated by reference in its entirety, provides a thorough discussion of passive diffusion sampling and describes one commonly used sampler arrangement.
As will be appreciated, typically, prior art passive diffusion samplers work by submersing a tubular low density polyethylene bag filled with analyte-free water into a ground water sampling bore hole. The polyethylene bag serves as a semi-permeable membrane that allows certain VOCs to diffuse through the membrane. Over time, an equilibrium is established between the VOCs in the bag and those in the groundwater. The sample bag is retrieved from the sample well after reaching equilibrium (typically after a two-week deployment) and the bags are opened and specimen vials are filled and sent to the laboratory for quantitative analysis. As will be appreciated by those of ordinary skill in the art, one major drawback with polyethylene bags is the inability of certain water contaminants, such as certain VOCs including certain ketones, ethers, and alcohols, to penetrate the membrane and be accounted for in the specimen samples sent to the laboratory.
Another known drawback of the Vroblesky et al. passive diffusion sampler described in the '743 patent involves the inherently fragile nature of polyethylene sample bags. Experience has shown that these bags were susceptible to tearing while being deployed or retrieved after deployment by snagging pointed edges of rocks and the like in the sample bores. The devastating loss of a sample bag after waiting two weeks for it to reach equilibrium is a significant problem in the art. Other prior artisans have suggested the use of a netting over the sampler to protect the bag from snags and tears. While this configuration has reduced the problem of snagging and tearing, there is still a long-felt, yet unresolved need in the art for a tear-free sampler.
The prior art suffers from yet another drawback that has been recognized by the present inventor. With the prior art samplers in use today, samples are collected by removing a bag cap and pouring them into sample vials. By design, these sample bags expose the water sample to the ambient air before the vial is sealed and sent for testing. The contamination of the sample by exposure to air is a problem the present inventor has recognized and solved through some embodiments of the present invention.
The foregoing underscores some of the problems with conventional passive diffusion samplers and bags. Furthermore, the foregoing highlights the long-felt, yet unresolved need in the art for a passive diffusion sampler that can sample for a broader universe of VOCs and contaminants in groundwater. Likewise, the foregoing highlights the long-felt, yet unresolved need in the art for a truly tear-free passive diffusion sampler system and bag. In addition, the foregoing highlights the inventor's recognition and need in the art for a passive diffusion sampler system capable of providing groundwater samples free from contamination by air.